The present invention relates to a heat-resistance increasing fabric sheet for an airbag that increases the heat resistance of an airbag, which is deployed and inflated by inflation gas discharged from an inflator.
An airbag apparatus is effective for protecting an occupant from an impact when an impact due to, for example, a collision is applied to the vehicle. The airbag apparatus generally includes an inflator, which discharges inflation gas through a gas outlet portion, and an airbag, which is deployed and inflated by the inflation gas.
In such an airbag apparatus, high-pressure inflation gas of 500° C. or higher is discharged from the gas outlet portion. The main body fabric portion, which forms the outer shape of the airbag, is generally formed by using polyamide fiber or polyester fiber. The melting points of polyamide and polyester are about 250° C. When the heat of high-temperature inflation gas is transferred, the main body fabric portion is carbonized instantaneously and the carbonized parts are scattered by the pressure of the inflation gas to form holes. One countermeasure against this is to place multiple heat-resistance increasing fabric sheets made of the same material as the main body fabric portion on a part of the inner surface of the main body fabric portion that is susceptible to the heat of the inflation gas. According to this countermeasure, the inflation gas is received by the multiple heat-resistance increasing fabric sheets. Thus, the heat of the inflation gas is unlikely to reach the main body fabric portion, suppressing the formation of holes in the main body fabric portion.
However, as the number of the heat-resistance increasing fabric sheets increases, it becomes more difficult to sew the heat-resistance increasing fabric sheets to the main body fabric portion. Also, as the number of the heat-resistance increasing fabric sheets increases, the airbag becomes not only less foldable but also heavier. Further, the bulk of the folded airbag becomes large, reducing the mountability of the airbag.
In this regard, heat-resistance increasing fabric sheets obtained by laminating a heat-resistant layer on a base fabric sheet have been developed (for example, Japanese Laid-Open Patent Publications No. 3-287433 and No. 7-277121). The heat-resistant layer is made of aluminum foil. The heat-resistant layer is denoted as “coating layer” in Japanese Laid-Open Patent Publication No. 3-287433 and “heat-resistant coating layer” in Japanese Laid-Open Patent Publication No. 7-277121. The base fabric sheet is denoted as “fabric” in Japanese Laid-Open Patent Publications No. 3-287433 and No. 7-277121.
A heat-resistant layer made of aluminum foil has a melting point (approximately 650° C.) higher than the temperature of inflation gas and increases the heat resistance of the heat-resistance increasing fabric sheet. On the other hand, when used alone, the aluminum foil constituting the above heat-resistant layer tends to degrade with age due to oxidation and electrolytic corrosion. For example, a metal (iron) ring retainer may be used when installing an inflator and an airbag in a driver's seat airbag apparatus. In such a case, if the heat-resistant layer contacts the ring retainer in a situation where moisture (including moisture in the air) is present, electrolytic corrosion may occur. Japanese Laid-Open Patent Publications No. 3-287433 and No. 7-277121 disclose no particular countermeasures against these problems.
Also, depending on the material of the base fabric sheet, the tensile strength and tear strength of the heat-resistant layer are not sufficient. Thus, in the above heat-resistance increasing fabric sheet, the heat-resistant layer may be peeled from the base fabric sheet during the deployment and inflation of the airbag.